1. Field of the Invention
The present invention relates to a voltage detection circuit and a voltage detection method.
2. Description of the Related Art
In order to operate an electronic circuit in a stable manner, a reset-voltage detection circuit is generally used. When a power-supply voltage supplied to the electronic circuit becomes equal to or lower than a reset voltage determined in advance, the reset-voltage detection circuit detects the power-supply voltage becoming equal to or lower than the reset voltage and resets a power-supply block employed in the reset-voltage detection circuit as a block which operates by receiving the power-supply voltage in order to supply a power to the electronic circuit.
FIG. 3 is an explanatory block diagram showing the existing reset-voltage detection circuit 10. As shown in the explanatory block diagram of FIG. 3, the existing reset-voltage detection circuit 10 for detecting a reset voltage employs a reset IC (Integrated Circuit) 11 and a power-supply block 12.
The reset IC 11 normally supplies a signal set at a high level to a CE terminal of the power-supply block 12 from an OUT terminal of the reset IC 11. Receiving a power-supply voltage denoted by reference notation. Power IN at a VIN terminal of the power supply block 12, the power-supply block 12 is made capable of operating by the high-level signal received from the reset IC 11.
When a power-supply voltage Power IN becomes equal to or lower than a reset voltage and the reset IC 11 detects this phenomenon through a VIN terminal of the reset IC 11, the reset IC 11 supplies a signal at a low level to the CE terminal of the power-supply block 12. Receiving the low-level signal received from the reset IC 11 at the CE terminal, the power-supply block 12 stops its operation, that is, the power-supply block 12 is reset.
When the power-supply block 12 is reset, the current consumed by the power-supply block 12 decreases. Thus, a voltage detected by the reset IC 11 at the VIN terminal rises. This is because a voltage drop D0 through a resistor R0 also decreases as well. When the voltage detected by the reset IC 11 at the VIN terminal rises to a level higher than the reset voltage, the low-level signal supplied by the reset IC 11 to the power-supply block 12 changes to the signal set at the high level. When the low-level signal supplied by the reset IC 11 to the power-supply block 12 changes to the signal set at the high level, the power-supply block 12 resumes its operation.
Let us think a case in which, at a point of time the power-supply voltage Power IN becomes equal to 2 V detected by the reset IC 11 through the VIN terminal, the reset IC 11 supplies the signal at a low level to a CE terminal of the power-supply block 12. Since the power-supply voltage Power IN is an analog voltage, the power-supply voltage Power IN may repeatedly vary its level back and forth over a small range such as a range of about 2 V±0.01 V. In this case, the signal output by the reset IC 11 to the power-supply block 12 also repeatedly changes back and forth over a small range.
In order to solve this problem, the reset IC 11 is normally provided with a hysteresis of about several tens of mV so that the signal output by the reset IC 11 to the power-supply block 12 does not repeatedly change back and forth over a small range even if the power-supply voltage Power IN repeatedly varies its level back and forth over a small range.
Depending on the configuration of the reset-voltage detection circuit 10, however, the power-supply voltage Power IN may repeatedly change back and forth over a range greater than several tens of mV. For example, the power-supply voltage Power IN may repeatedly change back and forth over a range of 2 V. In this case, by merely providing the reset IC 11 with a hysteresis, it may be impossible to cope with such large voltage changes. In order to solve this problem, the existing reset-voltage detection circuit 10 is provided with a capacitor for setting a large time constant for avoiding consecutive ON and OFF operations (or oscillations) of the power-supply block 12.